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The implementation of the correlated multi-jitter can be found in blender/intern/cycles/kernel/kernel_jitter.h . The functions are called cmj_sample_1D and cmj_sample_2D. The code is based on Andrew Kensler, &quot;Correlated Multi-Jittered Sampling&quot;, Pixar Technical Memo 13-01, 2013.
Here is how you can find this yourself:

Enabled Python Tooltips in the preferences (Edit &gt; Preferences &gt; Interface)
Hover over the sampling pattern drop-down in the UI until the tooltip appears. Take note of properties name, it is sampling_pattern.
Search for sampling_pattern in Blender's code. This can either be done in your local copy of the code or online through Blender's website or its GitHub mirror.
Find the code that implements the property first and try to figure out how it is used. You will notice that the property can be found in blender/intern/cycles/blender/addon/properties.py and the values that can be select for it come from enum_sampling_pattern.
The type that defines the enums that could be assigned can be seen in blender/intern/cycles/render/integrator.cpp and here. The name of the enum is SamplingPattern. The entry SAMPLING_PATTERN_CMJ is for the correlated multi-jitter.
Searching for the occurrences of SAMPLING_PATTERN_CMJ shows that it is used in blender/intern/cycles/kernel/kernel_random.h. The functions to compute the correlated multi-jitter are called cmj_sample_1D and cmj_sample_2D. Both are implemented in blender/intern/cycles/kernel/kernel_jitter.h .